Button #1 is a 1-piece "cast & spun" (lathed) White Tombac button. White Tombac is an alloy of copper, zinc, and arsenic. The design on the front was engraved by hand. It is from the latter 1700s through very-early 1800s.
Button #2 is a 2-piece button with iron back and thin stamped-brass "decorative" front, made for use on civilian clothing. Your specific version is from the 1830s through the rest of the 1800s.
Button #3 is one of the very earliest types of 2-piece buttons, dating from the 1700s. The front was soldered onto the back. The two holes in the back were there to allow superheated air to escape from inside the button during the soldering process.